Currently, commercially available luminescent materials for the field emission excitation may be divided into two main categories: sulfide systems, such as blue powders ZnS:Ag,Cl and SrGa2S4:Ce, green powder SrGa2S4:Eu, and red powder Y2O2S:Eu; and oxide systems, such as blue powder Y2SiO5:Ce, green powders ZnGa2O4:Mn, Y2SiO5:Tb and Y3Al5O12:Tb, and red powder Y2O3:Eu. However, the sulfide series has relatively poor stabilities. The oxide series has lower electrical conductivities than the sulfide series. Moreover, their luminescent intensities need to be improved. In order to improve the electrical conductivity of a luminescent material, the surface of the luminescent material may be coated with a conductive material, such as In2O3, SnO2, ZnO, etc., and luminescent materials having certain electrical conductivities are studied.